1. Field of the Invention
The present invention relates to an internal combustion engine of the type, in which a fuel is injected directly from an injection nozzle into a combustion chamber and more particularly to a Diesel engine.
2. Description of the Prior Art
In the Diesel engine of the direct fuel injection type, the piston has its top formed with a combustion chamber cavity, and an injection nozzle is arranged concentrically of the central axis of that combustion chamber cavity. In case the spray diverging angle of the injection nozzle is no less than 20 degrees, on the other hand, the aforementioned cavity is shaped to have a larger diameter at its deep portion than that in the open portion at the piston top so that the sprayed fuel may not impinge, just after it has been injected, upon the surface of the piston at the shortest distance.
In such internal combustion engine, when an injection nozzle is intended to have a larger spray diverging angle no less than 60 degrees so as to atomize and disperse the fuel spray in a manner to ensure satisfactory combustion, the combustion chamber cavity to be formed in the piston must have a still larger diameter at its deep portion than that in the open portion. As a result, the compression ratio of the engine is lowered, and the Diesel engine cannot attain a sufficiently high spontaneous ignition temperature immediately after it is started.